Chapter 8 Flower Disease

Section 3 Chinese Rose and Tulip Disease

（月季和郁金香病害）

1. Chinese Rose Black Spot （黑斑病） Roses are an important horticultural crop in the

word ， Black Spot is most familiar disease of rose.

The disease can cause almost complete defoliation of bushes by early fall. It produces a weakened bush on which cane dieback, stem canker, and winter injury can become severe.

1.1 Symptoms （症状） Circular black spots ranging from

1/16 inch to 1/2 inch in diameter appear generally on leaves’ upper sides. The spots are frequently surrounded by a yellow halo. Infected leaves characteristically turn yellow. They fall prematurely. This leaf spot can be distinguished from others by the fringed margin and consistently black color. Cane infection produces a reddish-purple spot. In many varieties, pale flower color is also indirectly caused.

1.2 pathogen

Diplocarpon rosae 放线孢属，半知菌 Acervuli 分生孢子盘 o n a leaf surface

1.3 Disease Cycle

Black spot is spread by splashing water. Infection occurs after leaves are wet for several hours. Therefore, the disease is more serious during periods of rainfall.

1.4 ControlReduce overwintering fungi:A preventive program for black sp

ot should begin with a thorough cleanup in the fall.

Diseased leaves on the ground should be raked and destroyed. All diseased canes should be pruned off by cutting several inches into good wood. These precautions reduce overwintering fungi.

Chemical control A fungicide program should start in the sum

mer just before leaves become spotted. From then until frost, the leaves may require a protective fungicide coating. When the leaves are growing rapidly or during rainy weather, it may be necessary to spray the plants two times a week. However, if growth is less rapid and rains are less frequent, spraying at 7 to 10 day intervals is usually sufficient. Proper timing is as important as the chemical spray. （ Chlorothalonil 百菌清， Captan 克菌丹， Lime-Sulfur 石硫合剂）

2. Chinese rose Powdery Mildew（月季白粉病）

This disease can cause young leaves to curl and turn purple. Young canes may be distorted and dwarfed. If seriously infected, they can die. Badly infected buds do not open.

月季白粉病是世界性病害，普遍发生，玫瑰、蔷薇也受其危害。此病一旦发生，降低切花产量及观赏价值。

2.1 Symptoms( 症状 )

Leaves, buds, and stems are covered with a white powdery coating.

2.2 Pathogen

Sphaerotheca pannosa (Wallr.) Lev.( 毡毛单囊壳菌 ) and S. rosae(Jacz)Z.Y. Zhao( 蔷薇单囊壳 ) . 属于子囊菌亚门单囊壳属。附属丝菌丝状较短。闭囊壳内只有一个子囊，椭圆形或长椭圆形，少数球形。无性态为粉孢属（ Oidium.sp ）

2.3 Rule of disease occurring The germ mainly overwinterring by the

mycelium in the bud, some areas overwinterring on the host by the ascocarp( 子囊果 ). The conidia can invade the anniversary in the greenhouse, taking advantage of air current dissemination directly to invade host. If the condition is suitable, conidia( 分生孢子 ) can produce for many times,and invade( 侵染 )many times.

2.4 Disease CycleThe white fuzzy growth on the leaf

surface contains thousands of fungal spores. Wind carries these spores to young leaves, causing more infection. Mildew diseases of other plants do not infect roses. Mildew develops rapidly during warm, humid weather.

2.5 Control Throughout the growing season, the infection

can be reduced through sanitation and fungicide application. Pruning and destroying all dead or diseased canes in the spring will reduce the initial fungus population. During the growing season, all diseased leaves should be destroyed. New growth is especially susceptible; therefore, a thorough spray or dust coverage of canes and upper and lower leaf surfaces (especially growing tips) is essential. Under most conditions, weekly applications are adequate; however, treat more often during rapid new growth, temperature fluctuations, and frequent rains.

3. Tulip breaking virus( 郁金香碎色花瓣病 )

3.1 Symptoms This is the most commonly se

en virus disease in tulips. It causes colour ‘breaking’ or streaking of the flower colour in pink, purple and red flowered tulips, but white and yellow flowered cultivars are not affected. It is particularly seen in late-flowering cultivars. Mottling( 斑纹 ) or striping( 条斑 ) of the leaves also occurs. Other symptoms include loss of vigour and poor flower production.

While tulip breaking virus is now known to be undesirable due to the loss of vigour it causes, some ‘broken’ tulip flowers can look very spectacular. In the 17th century, when the craze for tulips was at its peak in Holland and the cause of flower breaking was unknown, bulbs producing broken flowers were extremely desirable and valuable.

3.2 Biology

The disease is spread by several aphid( 蚜虫 ) species - Myzus persicae, Macrosiphum euphorbiae, and Aphis fabae.

3.3 Control

Control using insecticides is not very effective. Remove and destroy infected bulbs.

Avoid planting tulips close to lilies, which may harbour the virus without visible symptoms.

Cucumber mosaic virus

This disease is also seen in late-flowering cultivars. Symptoms appear as grey-brown sunken spots or rings on the bulb scales, which appear in storage. These bulbs produce deformed plants with chlorotic lesions on the leaves and aborted or damaged flowers. The disease is spread by aphids and also affects many other plants. Removal of the bulbs is the only control.